Warsaw: Artificial white light becomes eye-friendly

Research lead

A new class of organic substances discovered by scientists from the Institute of Physical Chemistry of the Polish Academy of Sciences and the Faculty of Chemistry of the University of Warsaw emits white light with continuous spectrum.

This provides experimental evidence that only single component luminophore will be necessary to construct eye-friendly light sources and displays.

Tired eyes and the impression that white is artificial are known to everyone who spends time in places lighted by popular non-thermal sources like fluorescent lamps or LEDs. Scientists from laboratories all over the world have been trying to eliminate these unpleasant side effects for years in their search for methods to recreate the sunlight which is the most natural light for humans.

Now scientists at the Institute of Physical Chemistry have shown that this objective can be achieved. “We have discovered a class of organic molecules emitting white light with continuous spectrum covering almost the entire visible range,” says Jerzy Karpiuk, who heads the research team.

It is also important that the emission of white light was obtained from one chemical compound with a very simple structure. White is created as a result of mixing of light waves of all lengths from the visual range, from approximately 420 to approximately 730 nanometres. The white colour of fluorescent lamps and similar artificial sources is created by the mixture of three colours only: red, green and blue, which come mainly from the non-continuous emissions of various inorganic luminophores. The light obtained in this way is devoid of many colour components and it is this effect that is responsible for the unpleasant visual sensations.

In addition, the need to use several substances lowers the energetic efficiency of light sources and complicates their manufacturing technology. The research team composed of Jerzy Karpiuk and Ewelina Karolak of the Institute of Physical Chemistry and Jacek Nowacki of the Faculty of Chemistry at Warsaw University observed white light emission continuously covering virtually the entire visible range.

Its source is crystal violet lactone (CVL), a substance produced in mass quantities and commonly used in copy paper as the so-called dye precursor. A CVL molecule has two fluorophores embedded in its structure and responsible for the emission of light: one for blue and the other one for orange. The contribution of each of them to CVL’s dual fluorescence heavily depends on the environment of the molecule which modifies the energetics of their excited states. “By properly adjusting the molecule’s surrounding, it is possible to control the parameters of the emission spectrum, and consequently, to change the colour or shade of the white light obtained,” says Karolak.

“The deeper significance of our research lies in the discovery that white fluorescence is a general property of CVL type molecules. The dependence of excited state energetics on molecular structure allows to predict the width, shape and other parameters of the dual fluorescence spectrum, and so enables the engineering and customised design of white fluorophores,” he added.

It turns out that even very small molecules can emit continuous white light. This fact opens up a new perspective for the production of eye-friendly light sources.